1. Field of the Invention
The present invention relates to a recording device suitable for use as, for example, electronic paper and a recorder.
2. Description of the Related Art
In recent years, information input means including a scanner and a digital camera, display devices including a monitor, and information output means including a printer have been used diversely along with the development of electronic information equipment. Information can be read directly from a display device such as a monitor. However, the display device such as a monitor is generally of an emissive type and therefore fatigues viewer's eyes. Moreover, since the resolution offered by the display device is not very high, direct reading of a document or still image from the display device such as a monitor may not be desired. Therefore, information recorded in electronic information equipment is often printed onto paper in order to read the information on the paper.
When information is printed onto paper and then read, the information on the paper is read by receiving reflected light. This little fatigues reader's eyes. Since the resolution offered by a printout is considerably high, the printout is highly discernible. Consequently, many users print a document, which is displayed on a monitor, onto paper so as to read the document.
However, the use of paper imposes a large load on an environment. Talking of the use situation of paper, for example, as soon as a received e-mail message is printed onto paper and read, the paper is disposed of. Thus, the paper is rather wasted.
Moreover, when a printer is used to produce a hardcopy of a document or an image, if the printer is an ink-jet printer, not only paper but also inks of primary colors such as cyan, magenta, and yellow, or of more colors are consumed. If the printer is a laser printer or an LED printer, toners of many colors are consumed. The use of the consumables required for printout onto paper imposes a large load on an environment.
A rewritable (re-recordable) type recording device called electronic paper has been proposed and under development. For example, an electrophoretic recording device, a twisted-ball type recording device, and a selective reflection type recording device employing a cholesteric liquid crystal have been proposed as reflective recording devices that have the capability of a memory.
The electrophoretic recording device has been disclosed in, for example, the proceedings of the IEEE (Vol. 61, No. 7, July 1973) or Nature (Vol. 394, No. 16, July 1988). The twist ball type recording device has been disclosed in, for example, the proceedings of the SID (Vol. 18, 3rd and 4th Quarters, 1977, p. 289).
The operation of selective reflection of the cholesteric liquid crystal was discovered from a cholesterol derivative in 1688. Moreover, a ferroelectric (smectic) liquid crystal is known to have the capability of a memory.
Japanese Translation of PCT International Application No. 6-507505 has disclosed a liquid crystal cell having chiral nematic liquid crystalline molecules dispersed in the network of a polymer. One form of the liquid crystal cell allows a liquid crystal to become reflective or transmissive (diffusible), and the liquid crystal is stable with a zero voltage in both the reflective and transmissive states.
Japanese Unexamined Patent Application Publication No. 9-105900 has disclosed an optically writable projection liquid crystal display device including a spatial modulator that has a photoconductive layer and a liquid crystal layer. Light is irradiated to the photoconductive layer, whereby information is written in the liquid crystal layer.
A recording device composed of a photoconductive layer and a cholesteric liquid crystal has been disclosed in “Reflective Display with Photoconductive Layer and Bistable Reflective Cholesteric Mixture” (SID 96 Applications Digest, p. 59). The recording device is used as a screen capture that is mounted on the screen of a personal computer in order to copy a screen image on the personal computer. Since the recording device preserves the copied screen image as if to be a memory, no power is consumed. Recording and deletion are achieved instantaneously.
Moreover, electronic paper composed of a photoconductive layer and a cholesteric liquid crystal has been disclosed in the collection of theses “Japan Hardcopy 2000” (p. 93–96).
The electronic paper obviates the necessity of a printer and paper, and is therefore inexpensive. Moreover, the electronic paper imposes no load on an environment. However, the recording devices that write information using light are susceptible to noise caused by extraneous light and likely to produce unclear images.